1. Field of the Invention
The invention relates to a torque-limited coupling element with an input part and an output part each rotatably mounted about a common rotational axis, and at least one connecting means which from a first position, in which the connecting means interconnects the input part and output part in a rotationally fixed manner subject to the formation of a positive engagement, can be transferred into a second position upon exceeding of a predeterminable limit torque acting between the input part and output part, in which the input part and output part are rotatably mounted relative to each one another.
2. Description of the Prior Art
Torque-limited coupling elements are employed for example in torque wrenches, preferentially in so-called self-triggering torque wrenches, which allow tightening screw connections manually or actuatorily with a defined predeterminable torque. Such a torque wrench is disclosed in DE 31 40 288 A1, which provides a sleeve-like tool housing which in the interior thereof a coil spring is rotated to provide a variably adjustable spring characteristic on the output side the spring bears against a central ball centrally mounted within the housing, which in axial and radial directions presses against three coupling balls arranged in an equal angular distribution. The balls are radially guided in a cage structure and become operationally connected against a tool bushing radially surrounding the cage structure provided on the output side subject to the formation of a positive engagement. When a predeterminable torque between drive-end tool sleeve and output-end tool sleeve provided through the variably adjustable spring characteristic is exceeded, the coupling balls are radially pushed inwardly via a guide slotted link. As a result, the positive engagement between coupling balls and the output-end tool bushing is released, so that no further force transmission via the torque wrench is possible.
In a secondary development stage, devices for the torque transmission provide for the use of magnetorheological fluids, which constitute suspensions of magnetically polarizing particles in a carrier fluid. The viscosity and also other rheological properties of the fluids can be variably adjusted quickly and reversibly in the presence of a magnetic field. Such a magnetorheological torque transmission device is disclosed in DE 10 2007 019 584 A, which in a particular manner is suitable for forming a coupling, break, locking or blocking device or as man-machine interface element. The device comprises at least two device parts relatively mounted rotatably about a common rotational axis, which are separated by at least one torque transmission gap that is filled with a magnetorheological fluid and penetrated by a variably adjustable magnetic field. With controlled increasing magnetic field strength the viscosity of the magnetorheological fluid increases and at the same time also the friction between both device parts rotatably mounted about the rotational axis, between which a maximum torque ultimately dependent on the magnetic field can be transmitted. By contrast, the purely mechanical solution described above making use of the coupling balls described there, is now replaced by the magnetorheological fluid as force-transmitting element. On the one hand, this has the advantage of a simpler design embodiment avoiding moveably mounted, force-transmitting elements while on the other hand the magnetorheological fluid is subjected to high mechanical shear loads, as a result of which the magnetorheological fluid is subjected to degradations capable of sustainably influencing the functional properties of the fluid.
A multiplicity of further coupling embodiments, which for the force transmission utilize the variable viscosity adjustment of magnetorheological fluids dependent on the magnetic field, are based on the same coupling principle. In this connection, reference is made to: WO 2006/086807 A1, DE 10 2007 015 053 A1 and DE 698 05 483 T2.
DE 11 2005 001 458 T2 describes a rotary fluid coupling which attempts to minimize the disadvantageous degradating effects of the shear loads that occur with the above coupling types on the magnetorheological fluid between the input parts and output parts of the coupling rotating relative to one another. A coupling device releasable in series with the drive element of the coupling is provided which prevents a torque transmission between input part and output part if required.